This invention relates to a control circuit for driving motor vehicles and more particularly to a control circuit for inititating the acceleration and deceleration of motor vehicles when preselected speeds of the vehicle are reached.
In general, internal combustion engines for motor vehicles present a high efficiency when operated at high loads, in other words, the rate of fuel consumption is small, while at low loads they present a decreased efficiency, that is, the rate of fuel consumption is large. Motor vehicles have preset engine outputs and transmission gear ratios so as to meet a wide range of driving conditions such as acceleration and hill-climbing. Therefore, even when driving on a flat road at a constant medium or low speed, the engine is in a light load condition, resulting in a low engine efficiency, i.e. the rate of fuel consumption has been large.
Conventional engines continue rotating even when vehicles are in a hill-descending, coasting or stationary condition, thus consuming a considerable amount of fuel. Also, when a motor vehicle is running on a flat road at a constant speed, but at the ordinary vehicle speed range, that is, below 100 km/h, the engine load is light, particularly at low speeds, so that the engine efficiency is low, resulting in a large rate of fuel consumption.
In an attempt to eliminate the above-mentioned drawbacks, there has been proposed a fuel-saving driving apparatus for internal combustion engines (U.S. Patent application Ser. No. 653,027) which includes a one-way clutch provided before or after the transmission to allow actuation only from the engine side so that, when the rotational frequency on the driven side is higher, only the driven side is kept freely rotatable, and in which there is provided a system to allow the engine to start when the driver steps on an accelerator pedal and to stop when the pedal is released, whereby through pedal operation the engine is intermittently operated in a high load condition which affords a high efficiency. The average engine output is adjusted by changing the ratio of time between operation and stop to thereby save fuel.
When such a fuel-saving driving apparatus for internal combustion engines is used, a motor vehicle is accelerated in the region of high engine efficiency, that is, low fuel consumption rate, to a speed greater than the desired speed. There after, the accelerator pedal is released to stop the engine while the vehicle is allowed to coast to a speed less than the desired speed, where, again, the accelerator pedal is depressed to start the engine and the vehicle is accelerated in the high efficiency region. This operation is continuously repeated so as to give an average speed equivalent to the desired speed, whereby it becomes possible to save fuel.
As is apparent from what has been summarized above, however, in such fuel-saving driving apparatus for internal combustion engines the driver himself compares the vehicle speed with the desired speed at all times and depresses or releases the accelerator pedal accordingly to the control inititation of vehicle acceleration and deceleration. This requires an extra attentiveness of the driver and causes dispersion because the judge is a human being. Thus, the vehicle is not always running in the optimum driving condition when viewed from the standpoint of fuel-saving driving.